The present application relates to a system and method for using deuterium (or proton) cluster (D- or p-cluster) technology for thin films as an intense pulsed neutron source.
The use of a film or foil as a source of particles when struck by a laser has been considered by several researchers with respect to fast ignition (FI) fusion. FIG. 1 illustrates a previously proposed proton-driven fast-ignition system 1 in which a petawatt laser 2 is focused on a backside (laser-facing side) of converter foil 3 to create an energetic ion beam (here, protons). As shown in FIG. 1, the protons 4′ come from a hydrogenous coating on the converter foil 3 surface. The protons 4′ create a hot spot 6 that within a pre-compressed fuel pellet 8 containing deuterium and tritium. Fusion reactions created in the hot spot heat up the remaining compressed fuel, causing it to fuse as well.
FIG. 2 illustrates a Hohlraum-based proton fast ignition concept. In this design, the laser 2 is focused on a target (shaped) foil 3′, which directs the protons 4′ against a pre-compressed fusion fuel pellet formed via x-ray compression within the Hohlraum, creating a hot spot 6 that initiated fusion reaction that spread (“propagate”) throughout the fusion fuel within the pellet.
Following early experiments on laser-acceleration of electrons, protons and carbon ions for fast ignition, some studies were performed, including those described in Hatchett, S. P., et al. Electron, photon, and ion beams from the relativistic interaction of Petawatt laser pulses with solid targets. in The 41st annual meeting of the division of plasma physics of the american physical society. 2000. Seattle, Wash. (USA): AIP; Maksimchuk, A., et al., Forward Ion Acceleration in Thin Films Driven by a High-Intensity Laser. Physical Review Letters, 2000. 84(18): p. 4108; and Krushelnick, K., et al. Energetic proton production from relativistic laser interaction with high density plasmas. in The 41st annual meeting of the division of plasma physics of the american physical society. 2000. Seattle, Wash. (USA): AIP.
These studies considered an accelerated deuteron beam to improve the ability of focusing on the hot spot volume. However, problems with making a suitable deuteron containing converter foil hampered these studies. These problems have now been addressed in the use of a “cluster” type deuterated converter foil technique for FI, as described in the Related Application section, and this design appears to be a very valuable approach to ion-beam driven FI. However, the use of cluster-type deuterated foils to create a neutron source for neutron beams has not previously been considered.
Historically, pulsed neutron beams have been used for a variety of applications, including medical isotope production, medical irradiations, and study of neutron damage to materials. Such neutron beams may also be applied in an increasing manner to homeland security uses. In the past, concepts for a source of such pulsed neutron beams have generally relied on accelerator-target concepts or on plasma discharges such as those produced by a dense plasma focus device. Due to the relatively low ion currents achieved with an accelerator and inefficiencies in plasma methods, resulting neutron source strengths are limited.
To increase yields, advanced plasma focus designs and high current diode accelerators that provide higher ion currents have also been studied. Alternatively, an ion and target combination to provide a spallation neutron source has been studied. For example, proton beams have been accelerated by a Synchrotron onto a heavy metal target, such as mercury or tungsten target, to produce neutrons with an energy spectrum of average energy of about 5 MeV neutrons. Currently, this approach offers about 1014-1015 protons per pulse at the target, and receives about a 1012 neutron per pulse yield. However, better sources of neutrons are desirable.